The ability of a surgical patient to recover from trauma and resist infection depends in part of his ability to make new proteins at optimum rates. This proposal is concerned with using a 15N labelled amino acid as a tracer to estimate the rate of human protein synthesis rates in the whole body, certain gastrointestinal tissues obtained by biopsy during medically indicated surgery and plasma proteins (albumin, fibrinogen, etc.). A 15 N analysis will be done by optical emission spectroscopy. First, the synthesis rates will be determined in a series of normal healthy human volunteers. These values will then be compared with values obtained with a group of surgical patients. The aim is to measure some of the changes caused in human protein synthesis by (1) trauma, (2) cancer, and (3) the effects of nutritional status and intravenous hyperalimentation on (1) and (2). Concomitantly parallel studies will be done in the rat.